1. Field of Disclosure
The present disclosure relates in general to valve bonnets, and more particularly to a bonnet that can assist in closing a valve.
2. Description of Related Art
A gate valve is a valve having a body and a bore through the body. A gate is positioned transverse to the body and moves linearly to obstruct flow through the bore or allow flow through the bore. Gates typically have an aperture that aligns with the bore to allow flow. The gate is sometimes moved, or actuated, by a valve actuator.
The valve actuator can be a pneumatic diaphragm and/or piston, electric, hydraulic or other conventional type actuator that urges a stem downward toward the valve to open the valve. A bonnet can be located between the valve and the valve actuator. The bonnet can be attached to the valve and a valve stem can extend through the bonnet. Over time, valves may develop excessive gate drag, making it impossible for the actuator to move upward and fully close the valve. Silt and debris can become trapped in a valve. In addition, damage at the gate and seat interface and excessive wear can make it difficult or impossible to fully close the valve. There may be times when an actuator does not have enough bonnet stem thrust or spring force to fully close a valve due to changing field conditions.
Also, during oil and gas production, wirelines or tubular members are often lowered through some type of gate valve. Ideally, the wireline or tubular members are removed from the well before the gate valve is closed. However, in some situations wireline or tubular member removal prior to valve closure is not possible and the gate valve is closed on the wireline or tubular member. Some actuators can provide sufficient force to cut wirelines or tubular members. However, not all valves are designed to do so and in an emergency situation, a wireline or tubular member running through the valve may need to be cut to close the valve. The safety of field operations can be jeopardized when a valve is left in a semi-open position because the actuator cannot apply the force required to close the valve completely.
Some current solutions for providing additional closing forces for these circumstances include using double acting actuators or wire cutting actuators. However, these are complicated and costly mechanisms.